We investigated cancer incidence in a cohort of 16,434 underground uranium miners from the Czech Republic. Eligible miners worked at least one year underground prior to January 1, 1976, and were alive and living in the Czech Republic on January 1, 1977. The cohort was followed for cancer incidence and mortality through December 31, 1992 by linking with the Czech cancer registry. Detailed records on daily work location and radon levels, smoking, dusts, and gamma radiation were obtained for a 2,000-person stratified random sample of the cohort and all cancer cases for use in case-cohort analyses. Cancer follow-up was extended through 1998 to increase the number of miners with cancers of sites other than the lung for inclusion in case-cohort analyses. Lung cancer was diagnosed in 752 miners through 1992. Fifty-six percent of miners began mining after 1960 when industrial hygiene measures substantially reduced radon exposure. Cumulative exposure was less than 50 WLM for 72% of the cohort. Miners had a more than two-fold risk of developing lung cancer. Age- and calendar year-adjusted relative risks comparing exposed miners to those with fewer than 5 WLM showed increasing risk with increasing levels of exposure. Preliminary case-cohort analysis confirms that the radon-associated risk for lung cancer is not explained by smoking or dust in the mines although dust exposure and smoking are both associated with lung cancer risk in this cohort. Comprehensive models of dose-response relationships between radon and lung cancer confirm the estimates derived from pooled studies of lung cancer mortality. The results from this study provide new information on risk associated with low level exposures, at doses that are consistent with those that could be achieved by long-term residence in a high radon home. [unreadable] [unreadable] Cancer of sites other than the lung was diagnosed in 1100 miners. Risk was increased for some cancers including leukemia, and cancers of the larynx, pancreas, liver, stomach, and colon and rectum, but the absence of consistent dose-response trends for cancers other than hematopoietic cancers points to factors other than radiation. In a case-cohort analysis of risk for hematopoietic cancers, radon and gamma irradiation appear to be independent risk factors for hematopoietic cancers in general and leukemia specifically. Although chronic lymphocytic leukemia (CLL) has been thought to be the only leukemia subtype that is not related to radiation, risk for CLL was significantly increased at exposures above 50 WLM for radon and 20 mSv for gamma radiation versus below and in a continuous analysis.